1. Field of the Invention
The present invention relates to a transcription plate for forming an orientation layer for a liquid crystal display, and more particularly to a transcription plate capable of forming the orientation layer with uniform thickness.
2. Description of the Prior Art
As generally known in the art, a liquid crystal display presents an image by making use of the optical properties of liquid crystal, which vary according to application of voltage. The liquid crystal display comprises a liquid crystal panel including a pair of substrates and liquid crystal filled into a space formed there between; and a printed circuit board for applying electrical signal to the liquid crystal panel.
In the liquid crystal display, molecules of liquid crystal should be aligned in a certain direction so as to obtain uniform brightness and high contrast ratio. For the purpose of aligning the molecules of the liquid crystal in a certain direction, an orientation layer has been formed by coating an orientation agent, such as polyimide onto inner surfaces of the substrates.
FIG. 1 is a perspective view of a conventional apparatus for coating orientation layer.
Referring to FIG. 1, a dispenser 50 and an Anilox roll 30 is shown. Using the dispenser 50, the orientation agent, such as polyimide is applied onto the Anilox roll 30. Here, the polyimide can be coated on the Anilox roll 30 with thinness and uniformity with an aid of a doctor blade 40. Afterward, the coated polyimide is printed onto a transcription plate 60 with a predetermined pattern, such as an Asahi Kasei photosensitive resin plate (APR plate), and then the polyimide printed on the transcription plate 60 is coated on the substrate 10 to form the orientation layer by the rotating action of coating roll 20.
As such, there must be provided a transcription plate (i.e., APR plate; Asahi Kasei Photosensitive resin plate) made from polymer material in order to form the orientation layer.
FIG. 2 is a plan view and a front view of a conventional transcription plate for forming an orientation film. FIG. 3 is a cross-sectional view of an orientation layer formed by the transcription plate for forming orientation layer according to the prior art.
As shown in FIG. 2, the conventional transcription plate for forming the orientation layer is a two-layered type including a base film 62 made from rubber material and a photosensitive resin plate such as an APR layer 64. The number of dots per line is 400 per an inch. Here, a diameter d of dot 66 is about 42 μm and a pitch between dots 66 is about 62 μm. Those dimensions are same over the whole area of the substrate, regardless of being within or outside of the active area defined by a phantom line.
Referring to FIG. 3, using the transcription plate 60 on which the orientation agent 70, such as polyimide is printed, the orientation agent 70 is coated onto the active area 12 of the substrate 10 to form the orientation layer 14.
However, the transcription plate for forming orientation layer according to the prior art includes such problems as listed below.
In the prior art, when forming the orientation layer on the substrate, the greater coating pressure acts upon an edge area of the transcription plate than any other area. Here, the coating pressure corresponds to the pressure between the transcription plate and the substrate and presents a degree of pressure on the substrate by the transcription plate.
Accordingly, as shown in FIG. 3, a thickness of the orientation layer formed along an edge area A of the transcription plate tends to become relatively greater than any other area. As such phenomenon development, it leads to the conglomeration of the orientation agent. As a result, a cell gap enlarges within an area where the edge area A outside of the active area 12 of the transcription plate overlaps with to a sealing line (not shown), thereby resulting in a defective cell gap.